1. Field of the Invention
The present invention relates to a strontium titanate (SrTiO3) dielectric ceramic, and a laminated ceramic capacitor configured with the use of the dielectric ceramic.
2. Description of the Related Art
SrTiO3 dielectric ceramics are preferably used in capacitors for temperature compensation since the capacitances of capacitors configured with the use of these dielectric ceramics have good linearity for their temperature coefficients. Furthermore, SrTiO3 dielectric ceramics are also used in high-voltage capacitors.
However, SrTiO3 dielectric ceramics generally have low dielectric constants, and thus have the defect of difficulty in reduction of the size of capacitors configured with the use of such dielectric ceramics.
In order to eliminate the defect mentioned above, a dielectric ceramic as described in, for example, Japanese Patent Laid-Open No. 7-45122 (Patent Document 1) has been proposed. The dielectric ceramic described in Patent Document 1 contains SrTiO3 as its main component, and further includes PbTiO3, Bi2O3, etc. PbTiO3 and Bi2O3 act to increase the dielectric constant of the dielectric ceramic.
However, PbTiO3 and Bi2O3 decrease the resistance to reduction of dielectric ceramic material. Therefore, PbTiO3 and Bi2O3 are not always suitable for constituting dielectric ceramic layers in laminated ceramic capacitors which have internal electrodes containing a base metal as their main components. From this aspect, it is not easy to increase the dielectric constants of SrTiO3 dielectric ceramics.
Furthermore, Patent Document 1 discloses the addition of various additives to SrTiO3 dielectric ceramics, including SnO2, for improving the withstand voltage. However, Patent Document 1 describes that the increase in the added amount of SnO2 decreases the dielectric constant. Also from this point of view, increasing the dielectric constant of the SrTiO3 dielectric ceramics is not simple.